Automatic driving wheel change-over apparatus

ABSTRACT

An automatic driving wheel change-over apparatus designed to automatically effect a change-over between two wheel drive mode and the four wheel drive mode of a vehicle in accordance with the surface conditions of a road. When the difference in speed between the front and rear wheel exceeds a predetermined value during the two wheel drive, a clutch is operated for a predetermined time TM 0 , and when the clutch is operated more than four times during a predetermined time TI 0  which is longer than the time TM 0 , the clutch is operated continuously for a predetermined time TH 0  which is longer than the time TM 0  thereby holding the vehicle in the four wheel drive mode.

BACKGROUND OF THE INVENTION

The present invention relates to an automatic driving wheel change-overapparatus and, more particularly, to an apparatus for automaticallyeffecting a change-over between a two wheel drive mode and a four wheeldrive mode of a vehicle in accordance with the surface conditions of aroad.

In the case of four wheel drive vehicles which have been used widely,the change-over between the two wheel drive mode and the four wheeldrive mode is accomplished manually so that the driver must make askilled judgement in accordance with the road surface condition, and thejudgement and the corresponding operation are troublesome.

A vehicle has been disclosed in Japanese Patent Kokai (Laid-Open) No.148,622/80 wherein, when a slip is detected during the operation, thedrive of the vehicle is changed over automatically to the four wheeldrive mode and the drive is changed back to the two wheel drive modeupon a disaperance of the detected operation condition.

In the case of ordinary automotive vehicles, for ease in driving it isdesirable that a vehicle is capable of and automatic change-over betweenthe four wheel drive mode and the two wheel drive mode while inoperation. Thus, a control system is conceivable in which a vehicle isbasically operated in the two wheel drive mode so that when thedifference in number of revolutions between the front and rear wheelsexceeds a predetermined value, it is determined that a slip is developedand the road surface is bad, thereby causing the vehicle to be operatedthe four wheel drive mode for a predetermined period of time. However,this system is disadvantageous in that, when the vehicle is running on along snow-covered road, gravel road or the like, the change-over betweenthe two wheel drive mode and the four wheel drive mode is repeatedlyeffected so that the clutch is thermally overloaded and the wear of theclutch increases thereby reducing the life of the clutch is reduced.

SUMMARY OF THE INVENTION

It is the primary object of the present invention to provide anautomatic change-over apparatus for vehicles in which the change-overbetween the two wheel drive mode and the four wheel drive mode isautomatically effected in accordance with the road surface conditionsand the number of occurrences of the change-over is reduced as much aspossible, thereby protecting the clutch and improving the drivabilityand running characteristic of the vehicle.

To accomplish the above object and other equally important objects, inaccordance with the invention there is provided an automatic drivingwheel change-over apparatus for a four wheel drive vehicle capable ofautomatically effecting the change-over between the four wheel drivemode and two wheel drive mode through the control of the clutch. Theapparatus comprises a front wheel speed sensor for detecting the numberof revolutions of the front wheels, a rear wheel speed sensor fordetecting the number of revolutions of the rear wheels, a control unitand a clutch for effecting the change-over between the two wheel drivemode and the four wheel drive mode, whereby the control unit engages theclutch so as to operate the vehicle in a four wheel drive mode for agiven period of time when the difference in speed between the front andrear wheels obtained from the outputs of the front wheel speed sensorand the rear wheel speed sensor exceeds a given value, and the controlunit also memorizes the number of times of change-over operation of theclutch in a given time interval longer than the given time period tocontinuously hold the clutch in the coupled position when the number oftimes of the change-over operation exceeds a given number.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of an embodiment of an automatic drivingwheel change-over apparatus according to the present invention.

FIG. 2 is a schematic diagram showing details of a control unit shown inFIG. 1.

FIG. 3 is a waveform diagram depicting the operation of themicrocomputer shown in FIG. 2.

FIG. 4 to 6 are flow charts showing the operation flow of themicrocomputer.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring now to the drawings wherein like reference numerals are usedthroughout the various views to designate like parts and, moreparticularly, to FIG. 1, according to this figure, a driving force of anengine 1 rotates front wheels 3 of a vehicle through a transmission 2with the front wheel drive constituting a basic operation mode of thevehicle. The driving force of the engine 1 rotates a shaft 5 by way ofthe transmission 2 and a clutch 4 for change-over between the two wheeldrive mode and the four wheel drive mode, and the rotation of the shaft5 rotates rear wheels 7 by way of a differential gear 6. The number ofrevolutions of the front wheels 3 is detected by a front wheel speedsensor 8 and the number of revolutions of the rear wheels 7 is detectedby a rear wheel speed sensor 9. The outputs of the front wheel speedsensor 8 and the rear wheel speed sensor 9 are supplied to a controlunit 10 so that, in accordance with the outputs of the front wheel speedsensor 8 and the rear wheel speed sensor 9, the control unit 10 performsthe required counting, computing, and decision-making operations, and anoutput of the control unit 10 is supplied to an actuator 1 whichactuates the clutch 4.

As shown in FIG. 2, the control unit 10 is designed so that the outputof the front wheel speed sensor 8 is applied to a microcomputer 16through a waveform reshaping circuit 12 and a counter 13, and the outputof the rear wheel speed sensor 9 is applied to the microcomputer 16through a waveform reshaping circuit 14 and a counter 15. The output ofthe microcomputer 16 is applied to the actuator 11 by way of a driver17.

Assuming that N_(F) represents the front wheel speed obtained from theoutput of the front wheel speed sensor 8 and N_(R) represents the rearwheel speed obtained from the output of the rear wheel speed sensor 9,if |N_(F) -N_(R) | becomes greater than a given speed difference ΔN, themicrocomputer 16 automatically changes the vehicle drive from the twowheel drive mode to the four wheel drive for a time. TM_(O) stored inthe memory of the microcomputer 16 as shown in FIG. 3. After the fourwheel drive mode has been automatically changed to the two wheel drivemode at the expiration of the time. TM₀, if the value |N_(F) -N_(R) |again exceeds the given speed difference ΔN, the two wheel drive mode isautomatically changed-over to the four wheel drive mode for the the timeperiod TM₀. It is arranged so that if the change-over from the two wheeldrive mode to the four wheel drive mode is effected for example, fourtimes within a predetermined time TI_(O) which is longer than the timeTM₀, then the microcomputer 16 operates so as to maintain the four wheeldrive mode for a given time TH₀ which is longer than the time TM₀.Preferably, the time TM₀ is ten seconds, the time TI₀ forty seconds andthe time TH₀ is five minutes.

The detailed operation flow of the microcomputer 16 is shown in FIGS. 4to 6. Flag symbols and counter symbols are first defined as follows:

FN=ΔN A flag which is set when |N_(F) -N_(R) |≧ΔN;

FH=four wheel drive hold flag which is set when the number of clutchoperation exceeds four

FS1, FS2=one second flags which are each set at intervals of one second,

FTS=ten second flag which is set at intervals of ten seconds;

FF=first operation flag which is set when the clutch is engaged for thefirst time after it has been disengaged;

FC=count flag which is set when the clutch is engaged for the first timeafter the expiration of the predetermined time period TI₀ ;

CN=number of clutch operations counter;

TH=counter for counting the hold time after four clutch operations;

TI=counter for counting the time after the time that the flag FC is set;

TM=counter for counting the time after the flag FF is set.

The tasks imposed on the microcomputer 16 may be roughly classified asfollows:

(1) Detection of N_(F) and N_(R) and decision-making on |N_(F) -N_(R)|≧ΔN;

(2) Counting of TM and decision-making on TM=TM₀ ;

(3) Counting of CN and decision-making on CN=4;

(4) Counting of TI and decision-making on TI=TI₀ ;

(5) Decision-making on the hold, counting of TH and decision-making onTH=TH₀ ;

(6) Outputting a control signal.

The software organization of the microcomputer comprises an interruptroutine INT1 for counting N_(F) and N_(R), a timer interrupt routineINT2 for detecting N_(F) and N_(R) and making a decision on |N_(F)-N_(R) |≧ΔN as shown in FIG. 5 and a main routine shown in FIG. 6 forexecuting the above mentioned tasks (2) through (6).

Each of the counters 13 and 14 comprises a four-bit counter and theinterrupt routine shown in FIG. 4 is started each time the counterreaches the full count. then the interrupt is initiated, a step 21increases by one a four-bit front wheel counter in the microcomputer 16when the interrupt is caused by the counter 13 and increases by 1 a4-bit rear wheel counter in the microcomputer 16 when the interrupt iscaused by the counter 15. As a result, the front and rear wheel countersin the microcomputer 16 respectively form the higher four-bits of thecounters 13 and 15, thereby providing an eight-bit front and rear wheelcounters. After the step 21 has increased the counter by one, a step 22returns the processing to the main routine.

The timer interrupt routine INT 2 shown in FIG. 5 is initiated atintervals of 10 m sec. When the timer interrupt routine INT 2 isinitiated, a step 23 determines whether the interruptions reaches tentimes. If the decision is YES, a step 24 fetches a front wheel speedN_(F) from the counter 13 and the front wheel counter and a rear wheelspeed N_(R) from the counter 15 and the rear wheel counter. Then, a step25 determines whether |N_(F) -N_(R) |≧ΔN. If the decision is YES, a step26 sets the ΔN flag FN and generates a clutch-on command to operate thevehicle in the four wheel drive mode and then the above four countersare reset at step 26B. If the decision of the step 25 is NO, a step 27resets the flag FN and then a step 26B resets the counters provided withN_(F), N_(R). The contents of the flag Fn are used by the main routine.When the step 23 judges to be NO, the routine jumps to a step 28A,wherein a count of the one second counter is increased by one and a step28B determines whether one second has elapsed. In other words, thisinterrupts routine is initiated at intervals of 10 m sec. and thus onesecond is reached when the count of the one second counter reaches onehundred. The step 28B determines whether the count of the 1 secondcounter has reached one hundred. If the decision of the step 28B is YES,a step 29 sets the one second flags FS1 and FS2 and also resets the onesecond counter. Then, a step 30A increases the count of the ten secondscounter by one and a step 30B determines whether the ten seconds counterhas attained ten seconds or the count of the ten seconds counter hasreached ten. If the decision is YES, a step 31 sets a ten seconds flagFTS and a step 32 returns the processing to the main routine. If thedecision of the step 28B or 30B is NO, the step 32 returns theprocessing to the main routine. The one second flags FS1 and FS2 areused by the timer counters TI and TM of the main routine, and the tenseconds flag FTS is used when the timer counter TH of the main routinecounts the time.

With the flow of the main routine shown in FIG. 6, first a step 34clears the RAM and performs the initialization of the interrupt flags,etc., and the next step 35 determines whether the hold time is going on.If FH=1, it is an indication that the hold time TH₀ of FIG. 3 is goingon and in this case, a step 36A determines whether the ten seconds flagFTS has been set. If the decision is YES, a step 36B increases the countof the hold time counter TH by 1 and also resets the ten seconds flagFTS, and then a step 36C determines whether the contents of the holdtime counter TH have attained the hold time TH₀. If the decision is YES,the processing is returned to the beginning of the main routine so thatall the elements are reset and the processing is started again from theinitialized state. If the decision of the step 36A or 36C is NO, then astep 46 generates a clutch-on signal and the processing is returned tothe step 35. In the preferred embodiment, the hold time TH₀ is preset tofive minutes. Since the flag FTS is set by the step 31 in FIG. 5 atintervals of ten seconds, the decision of the step 35 becomes YES atintervals of ten seconds and the decision of the step 36C becomes whenthe count of the timer counter TH reaches thirty.

If the step 35 determines that FH=0 or it is not the hold period, a step38 makes a decision on the number of clutch operations so that if CN=4,step 37 sets the hold flag FH and the step 46 generates a clutch-onsignal. Contrary, if CN≠4, a step 39 makes a decision on the timecounter TI. If TI≧TI₀, a step 41 clears the clutch operations counterCH, resets the count flag FC and then transfers to a step 42. If TI<TI₀,a step 40A determines whether the one second flag FS1 has been set. Ifthe decision is YES, a step 40B increases the count of the timer counterTI by one and also resets the flag FS1, and then a step 40C sets thecount flag FC. If the decision of the step 40A is NO, the processingproceeds to the step 40C. Since the one second flag FS1 is set by thestep 29 at intervals of one second, the decision of the step 40A becomesYES at intervals of one second and the count of the timer counter TI iscorrespondingly increased. In this embodiment the time TI₀ is selectedto be forty seconds and thus the decision of the step 39 becomes YESwhen the count of the time counter TI reaches forty.

If the step 42 determines that the first operation flag FF is 1, a step43 makes a time decision on the timer counter TM. If TM≠TM₀, a step 45Adetermines whether the one second flag FS2 has been set. If the decisionis YES, a step 45B increases the count of the timer counter TM by one,resets the 1 second flag FS2 and then transfers to the step 46. If thedecision of the step 45A is NO, it represents a condition where thecount of the timer counter TM has been increased finally and one secondhas not elapsed as yet and thus the step 45A transfers directly to thestep 46. If the step 43 determines that TM=TM₀, then a step 44 resetsthe first operation flag FF and transfers to a step 47 which in turngenerates a clutch-off signal. If the step 42 determines that FF≠1, astep 48 makes a decision on the ΔN flag FN so that if FN=1, a step 49sets the first operation flag FF and a step 50 clears the timer counterTM. Then, a step 51 increases the count of the clutch-on operationscounter CN by one and a step 52A determines whether the count flag FChas been set. If the decision is NO, it is an indication that theexpiration of the clutch-on operations count time TI₀ has beendetermined by the step 39 and the count flag FC has been reset by thestep 41, a step 52B clears the timer counter TI and transfers to thestep 46. If the decision of the step 52A is YES, it is an indicationthat the timer counter TI has not reached TI₀ and thus the step 52Atransfers directly to the step 46.

In the above-described flow diagrams, the flow of the main routine atthe points A, B, C, D, E, F and G, respectively, of FIG. 3 is asfollows;

The point A: step 35→step 38→step 39→step 40→step 42→step 48→step47→step 35;

The point B: step 35→step 38→step 39→step 40→step 42→step 43→step45→step 46→step 35;

The point C: step 35→step 38→step 39→step 40→step 42step 48→step 49→step50→step 51→step 52A→step 46→step 35;

The point D: step 35→step 38→step 37→step 46→step 35;

The point E: step 35→step 36→step 46→step 35;

The point F: step 35→step 36A→step 36B→step 36C→step 34→step 35;

The point G: step 35→step 38→step 39→step 41→step 42→step 48→step49→step 50→step 51→step 52A→step 52B→step 46→step 35.

From the foregoing it will be seen that in accordance with the inventionthe control is performed so that the clutch is operated for thepredetermined time, TM₀ when the speed difference between the front andrear wheels during the two wheel drive mode exceeds ΔN, and if the countof the clutch operation counter CN becomes four or more during thepredetermined time TI₀ the clutch is operated for the predetermined timeTH₀ thereby holding the four wheel drive mode. As a result, due to thefact that, upon occurrence, for example, of four automatic clutchchange-over operations, it is determined that a bad road surfacecondition continues for some time and the four wheel drive mode is heldfor a predetermined time, the number of clutch change-over operations isreduced and the danger of the clutch being thermally damaged is reducedand the wearing of the clutch 4 is also reduced. Also, in accordancewith the invention the number of clutch change-over operations isreduced thus reducing the hunting of the four wheel drive mode and thetwo wheel drive and improving the drivability and running characteristicof the vehicle.

While, in the embodiment, the holding of the four wheel drive mode iseffected when the clutch 4 is automatically changed over four times, itis needless to mention that the number of automatic clutch change-overoperations is not limited to four. Experimentally, the clutch must bechanged over at least three times and in this case it is sufficient ifthe value of TI₀ is at least three times that of TM₀.

As described hereinabove, in accordance with the automatic driving wheelchange-over apparatus of this invention the change-over between the twowheel drive mode and the four wheel drive mode can be effectedautomatically in accordance with the road surface conditions and thenumber of change-over operations can be reduced as far as possible,thereby protecting the clutch and improving the drivability and runningcharacteristic of the vehicle.

We claim:
 1. An automatic driving wheel change-over apparatuscomprising:first wheels and second wheels driven by an engine; clutchmeans for effecting a change-over between a drive by said first wheelsand a drive by said first and second wheels; first detecting means fordetecting a rotational speed of said first wheels; second detectingmeans for detecting a rotational speed of said second wheels; means fordetermining a difference between the rotational speed signalsrespectively detected by said first and said second detecting means isgreater than a predetermined value; first acuating means responsive toan output of said means for determining for acutating said clutch meansand to drive said first and second wheels for a predetermined timeperiod; counting means for counting a number of times said firstactuating means is operated during a second predetermined time periodwhich is longer than said first predetermined time period; and secondactuating means for actuating said clutch means for a thirdpredetermined time period which is longer than said first predeterminedtime period to thereby drive said first and second wheels when saidcounting means reaches a predetermined value.
 2. An apparatus accordingto claim 1, wherein said counting means is adapted to count up to atleast three.
 3. An apparatus according to claim 2, wherein said secondpredetermined time period is greater than three times said firstpredetermined time period.